DESCRIPTION(adapted from applicant's abstract): Recent studies have indicated that cholesterol is essential for normal brain development and that the central nervous system depends mainly on de novo cholesterol biosynthesis. We have shown that peroxisomes are essential for cholesterol biosynthesis, due to the fact that the entire pathway for the biosynthesis of farnesyl diphosphate (FPP) from mevalonate is exclusively found in peroxisomes. Therefore, peroxisomes must play a critical functional role in this process in the CNS. However, no information is available on the peroxisomal isoprenoid/cholesterol biosynthesis pathway in normal brain or on the compartmentalization of isoprene metabolism in the CNS. An animal model for Zellweger syndrome (i.e., a peroxisomal PEX2 knockout mouse) has been recently developed. These mice provide an important model to study the role of peroxisomal function in the CNS in the pathogenesis of the neurological abnormalities observed in these diseases. In this proposal we address the hypothesis that peroxisomes have a central role in isoprenoid/cholesterol biosynthesis in the CNS and that in PEX2 knockout mice, the isoprenoid/cholesterol biosynthesis in the CNS is significantly altered. To test this hypothesis the following specific aims are proposed: 1) To determine the role of peroxisomes in isoprenoid/cholesterol biosynthesis in normal neonatal mouse brain. The isoprenoid biosynthetic pathway in neonatal mouse brain will be analyzed by subcellular fractionation, activity and immunoblot analysis of the gradient fractions, and immunohistochemistry and in situ hybridization techniques. We will also determine if the relative distribution of peroxisomal and ER contribution to sterol/non-sterol biosynthesis changes during development. 2) To test for defects in lipid composition and cholesterol/dolichol metabolism in PEX2 deficient mice. We will determine how the regulation of cholesterol enzymes and the rate limiting steps in the pathway may be altered by the decompartmentalization of cholesterol synthesis due to the absence of peroxisomes. The studies are designed to ascertain whether there is a basis to implicate cholesterol in some of the neurologic defects observed in the Zellweger mouse. Thus a comparison of isoprenoid/cholesterol metabolism in the PEX2 deficient and normal animals can render insight into the mechanism(s) for the neurological phenotype seen in the knockout mice.